我正在嘗試\DateInterval從2個(gè)輸入字段中讀取a ，如下所示：public function buildForm(FormBuilderInterface $builder, array $options){    $builder        ->add('name', TextType::class, ['label' => "Name"])        ->add('duration', DateIntervalType::class, ['label' => false])    ;}public function configureOptions(OptionsResolver $resolver){    $resolver->setDefaults(['data_class' => NamedInterval::class]);}這是我的DateIntervalType::buildForm：public function buildForm(FormBuilderInterface $builder, array $options){    $builder        ->add('amount', IntegerType::class)        ->add('kind', ChoiceType::class, ['choices' => ['Year' => 'Y', 'Month' => 'M', 'Week' => 'W']])    ;}這是我嘗試過(guò)的變壓器：$builder->get('duration')->addModelTransformer(new CallbackTransformer(    function ($property) {        return new \DateInterval('P' . $property['amount'] . $property['kind']);    },    function ($property) {        /* compute $specString from $property assuming it's a \DateInterval */        /* ... */        return ['amount' => 1, 'kind' => 'W'];    }));因此，這是行不通的，我$property總是null在從表單數(shù)據(jù)轉(zhuǎn)換到表單數(shù)據(jù)后驗(yàn)證表單，\DateInterval而我甚至不確定我是否曾經(jīng)使用過(guò)從變壓器轉(zhuǎn)換\DateInterval成表單數(shù)據(jù)，我在做什么錯(cuò)呢？